Conventional heat pump equipment such as an air-conditioning apparatus and a water heater typically uses a vapor compression refrigeration cycle system using a multi-cylinder rotary compressor. Specifically, such heat pump equipment incorporates a refrigeration cycle formed by connecting a multi-cylinder rotary compressor, a condensor, a pressure reducing unit, and an evaporator by pipes to perform an operation in accordance with an application (e.g., air-conditioning or hot water supply).
In recent years, regulations for energy conservation of air-conditioning apparatus have been tightened in many countries, and the operation standard has been changed to that close to an actual load. In Japan, a conventional indication of efficiency improvement based on an average COP in cooling and heating was changed to an indication based on an annual performance factor (APF) on 2011. Energy conservation standards of air-conditioning apparatus and water heaters are expected to be changed to a new standard closer to an actual load. For example, the rated heating capacity necessary for starting an air-conditioning apparatus is assumed to be 100%, an always necessary heating capacity is about 10% to 50%, and efficiencies in this low-load region has a greater influence on an actual APF than the rated capacity.
For this reason, an on-off control has been employed for a long time as a unit for adjusting a cooling and heating capacity. This on-off control, however, has problems such as increased temperature control range, increased vibration noise, and a degraded energy saving performance. Consequently, to improve energy saving performance, for example, an inverter control that changes a rotation speed of an electric motor for driving a multi-cylinder rotary compressor has been widely employed in recent years.
Recent air-conditioning apparatus have been required to have a reduced start-up time and operate under severe environments (under low or high temperatures), and thus, a rated capacity to a certain level or higher has been needed. On the other hand, an always necessary capacity is small for heat-insulated houses that have currently been popular, and the capacity range in operation has increased. Consequently, the variable range of the rotation speed of the multi-cylinder rotary compressor by the inverter increases, and the rotation speed range where a high efficiency of the multi-cylinder rotary compressor is required tends to increase. Thus, it has become difficult for a conventional air-conditioning apparatus to continuously operate a multi-cylinder rotary compressor at a reduced rotation speed and maintain a high efficiency of the multi-cylinder rotary compressor under low-load capacity conditions.
In this situation, a multi-cylinder rotary compressor using a unit (mechanical capacity controlling unit) for mechanically changing an air volume attracts attention again. For example, Patent Literature 1 proposes a reciprocating multi-cylinder rotary compressor in which “a second compression mechanism part 2B in a multi-cylinder rotary compressor A includes a cylinder cutoff mechanism K for separating a tip edge of a second blade 15b from a peripheral surface of a roller 13b to attain suspension of compression operation in a second cylinder chamber 14b, and the cylinder cutoff mechanism includes a blade back chamber 16b housing a rear end of the blade and forming a closed space, a discharge pressure introducing passage 20 for introducing a discharge pressure to the blade back chamber 16b, a shut-off valve 21 for opening and closing communication of the discharge pressure introducing passage 20, and a biasing holder 18 that biases and holds the blade tip edge in a direction away from the roller peripheral surface.” In the multi-cylinder rotary compressor described in Patent Literature 1, the shut-off valve 21 is closed under a low load so that the blade back chamber 16b becomes a closed space, and thereby, a pressure difference between a front surface and a rear surface of the blade 15b (vane) is eliminated. The blade 15b (vane) is moved back by a piston and is attracted by a magnet provided in the blade back chamber 16b so that the blade 15b (vane) is separated from the piston. That is, in the multi-cylinder rotary compressor of Patent Literature 1, one compression mechanism part is set in an uncompressed state to reduce the flow rate of circulating refrigerant by half so that the compressor can operate without a reduction in the rotation speed of an electric motor, thereby achieving an increased compressor efficiency.
To reduce a load in start-up of a multi-cylinder rotary compressor, Patent Literature 2 proposes a “multi-cylinder rotary compressor which includes a hermetically sealed container having a high internal pressure and housing an electric element and a plurality of rotary compressor elements driven by the electric element, and in which a spring is provided at the back of a vane of at least one of the rotary compressor elements and draws the vane outward and a spring is provided at the back of a vane of another rotary compressor element and presses the vane inward.” That is, in the multi-cylinder rotary compressor of Patent Literature 2, the front end of a vane is separated from the outer peripheral wall of a piston when a pressure difference does not occur between the front surface and the rear surface of the vane, and when a pressure occurs between the front surface and the rear surface of the vane, the front end of the vane is pressed against the piston.